Disposable absorbent articles, such as diapers for babies and underwear for adults, are prevalent in the marketplace. Disposable absorbent articles have been gradually and steadily taking the place of reusable diapers made of cloth. Such absorbent articles typically comprise a liquid permeable topsheet, liquid impermeable back sheet, and an absorbent member interposed between the topsheet and the back sheet, each structure having a substantially rectangular shape. When worn, these structures form a front waist body portion located at the front waist of a wearer, and a rear waist body portion located at the rear waist of a wearer, where the rear waist body portion has at each side thereof a fastening member for fastening the absorbent article.
The above-described absorbent articles are particularly required to have satisfactory performance in leakproofness, breathability, and texture.
The absorbent articles are required to have an improved fastening function to provide improved leakproofness, and a number of proposals concerning this aspect have been made.
In particular, it is necessary that an absorbent article once worn be unfolded and then re-fastened so that any change of the absorbent member during use (whether the absorbent member is in a correct position or whether the absorbent member still has room for absorbing the body liquid, and the like) may be checked to confirm excretion. To this effect, improvement in the fastening function thereof has been demanded.
A fastening system adopted in conventional absorbent articles is comprised of a fastening member formed of an adhesive tape with an adhesive, where the fastening member is stuck to a landing member provided for reinforcement on the surface of the back sheet.
The problem of the conventional disposable diapers having such a fastening system is that, to ensure fastening (to prevent the fastening member from releasing during use) there is accompanied an increased difficulty in unfastening and re-fastening. In order to ensure fastening and yet allow unfastening followed by re-fastening, the landing member should have increased strength and, accordingly, the back sheet should also have increased strength, which makes the back sheet harder and rougher which in turn deteriorates the texture or the fit of the diaper when put on a wearer.
The size of the landing member to be provided on the back sheet is minimized because too large a landing member would give a poor fit. Also, such a large landing member would increase cost. If the landing member is too small, on the other hand, the adhesive tape is liable to be stuck to the surface of the back sheet where no landing member is provided due to a mistake during placement. This being the case, the back sheet will be broken when the adhesive tape is stripped off for re-fastening or when movement of a wearer imposes stress to the adhesive tape.
While an absorbent article is worn by a baby or even an adult, waste liquid excreted from the body (and held in the absorbent member) and body fluid evaporated from the skin covered with the absorbent article make the inside of the absorbent article stuffy, which facilitates diaper rash on the wearer. This is because "breathability" is required of an absorbent article.
To meet the above-described demands, various proposals on films (or sheets) useful as a back sheet have been made to date.
For example, Japanese Patent Publication No. 38011/93 discloses a finely porous sheet obtained by melt-kneading a specific crystalline polymer (e.g., polypropylene) and a specific compound (e.g., a mineral oil), causing phase separation while sheeting (cooling), and stretching the resulting sheet.
However, the finely porous sheet proposed is inferior in leakproofness, especially against low-surface tension liquids, such as urine.
Japanese Patent Laid-Open No. 47031/90 proposes a finely porous film obtained by melt-extruding a crystalline resin, cooling the extruded film under a pressure roll, and subjecting the film successively to heat treatment, stretching, and heat treatment. Japanese Patent Laid-Open No. 75151/90 proposes a finely porous film obtained by molding a crystalline polyproplyene resin into film under specific conditions and stretching the resulting film under specific conditions. Further, Japanese Patent Laid-Open No. 331306/93 proposes a porous film consisting essentially of polypropylene and polyethylene.
Although the films according to these proposals are all excellent at preventing leakage of low-surface tension liquids such as urine, they not only have poor tensile and tear strength but they have a rough texture and are not therefore applicable as a back sheet of absorbent articles.
"Texture" is an attribute required because the skin of babies is soft and sensitive to a little pressure or a sliding action. As above stated, a special reinforcement should be provided on the surface of the back sheet for allowing unfastening followed by re-fastening to check excretion, which results in poor texture. Under the present situation, therefore, no absorbent article that satisfies the requirements of leakproofness and breathability as well as texture has been proposed as yet.
In short, absorbent articles such as disposable diapers are required to be excellent in leakproofness, breathability, and texture. To satisfy these requirements, it has been desired for an absorbent article to have the following: a back sheet that is soft and yet is not broken even without special reinforcement and also leakproof against liquid and yet highly permeable to moisture, a fastening function that allows unfastening for re-fastening, soft surfaces which are to be brought into contact with the skin (corresponding, in the case of an absorbent article, to the side of the topsheet and the back sheet that is opposite to the side contacting the absorbent member), and a function of minimizing the contact area with the skin. None of the absorbent articles so far proposed satisfy these requirements fully.
Accordingly, an object of the present invention is to provide an absorbent article which has a good fit on a wearer, exhibits excellent leakproofness and breathability while worn, and has an excellent texture.